1. Field of the Invention
Apparatuses and manufacturing methods consistent with the present invention relate to an optical waveguide device which includes an optical waveguide part and an optical device mounting part on a substrate.
2. Description of the Related Art
Optical transceivers used in optical access markets are broadly divided into a microoptics type module composed of an laser diode (LD), a photo detector (PD), a thin film filter, and a lens, and a planar lightwave circuit (PLC) type module configured by making a silica waveguide on a silicon substrate and surface-mounting an LD and a PD. While both of them have advantages and disadvantages, the latter is more advantageous in terms of cost and delivery because it does not require optical axis adjustment. This mounting method which does not require optical axis adjustment is generally called a “passive alignment mounting”.
In passive alignment mounting, a planar position of an optical component against an optical waveguide chip is determined by performing image detection and recognition of alignment markers provided to both of them with infrared transmitted light. A vertical position of the optical component is determined by the height of a block called a pedestal. Because the pedestal height can be made with high accuracy, it is possible to match the height with an optical waveguide with high accuracy by mounting the optical component on the pedestal.
This kind of optical waveguide device is disclosed in Japanese Patent Number 2,823,044. FIG. 3 is an exploded perspective view showing a related art optical waveguide device disclosed in this patent. In FIG. 3, an optical waveguide device 50 includes an optical waveguide part 56, which consists of an optical waveguide forming layer 55 with lower cladding layers 521 and 522, a core layer 53, and an upper cladding layer 54 formed on a silicon substrate 51. The optical waveguide device 50 also includes a photonic device mounting part 57, which is configured by eliminating a part of the optical waveguide forming layer 55. A light emitting device 58 mounted on the photonic device mounting part 57 is optically connected to an end face of the optical waveguide part 56, which is exposed by the elimination of a part of the optical waveguide forming layer 55.
The photonic device mounting part 57 includes a pedestal block 59, an alignment marker 60 consisting of a lower cladding layer 521, a pedestal block forming mask 62 consisting of a chromium (Cr) film 61 provided on the pedestal block 59, and the light emitting device 58 which contacts the mask 62. The lower cladding layers 521 and 522, the core layer 53, and the upper cladding layer 54 are atmospheric chemical vapor deposition (CVD) films.
In other words, the optical waveguide device 50 is a formed by surface-mounting the light emitting device 58 on a PLC chip with an optical waveguide circuit.
FIG. 4 shows sectional views of a method of manufacturing the optical waveguide device of FIG. 3, where the operations proceed in order of FIG. 4(a) to (h). Hereinafter, an explanation will be given based on FIG. 3 and FIG. 4.
In FIG. 4(a), the lower cladding layer 521 is deposited as a first layer on the silicon substrate 51.
In FIG. 4(b), the chromium film 61, which later becomes a mask for forming the pedestal block, is patterned on the lower cladding layer 521. Here, the chromium film 61, which becomes a mask for forming the alignment marker required for mounting the light emitting device 58, is patterned.
In FIG. 4(c), the lower cladding layer 522 is deposited as a second layer.
In FIG. 4(d), the core layer 53, which becomes a core of the optical waveguide part 56, is deposited on the lower cladding layer 522, and the waveguide is patterned by dry etching.
In FIG. 4(e), an upper cladding layer 541 is deposited as the first layer for embedding the core layer 53 and reflow-processed at a high temperature. The upper cladding layer 541 consists of a low melting film. The temperature of the reflow process is generally between 800° C. to 900° C.
In FIG. 4(f), an upper cladding layer 542 is deposited as the second layer to complete a waveguide structure.
In FIG. 4(g), a chromium film 63 and a photoresist film 64 are deposited, and are patterned so that only the chromium film 63 remains on the optical waveguide forming layer 55 as the optical waveguide part 56. Lastly, the end face of the core layer 53 is exposed by dry etching by using the chromium film 63 as an etching mask. Also, the pedestal block 59 and alignment marker 60 are formed by using the patterned chromium film 61 as an etching-stop mask 62 to complete the optical waveguide device.
Thereafter, elimination of the chromium film, and film formation and patterning of an insulating film and an electrode metal are performed as required. For instance, the chromium film 63 is eliminated in FIG. 4(h).
In the optical waveguide device 50, the height of the core layer 53 of the optical waveguide part 56 and the pedestal block 59 is only controlled by the accuracy of a film formation apparatus. The accuracy of the film formation apparatus is around 1%, due to variations in a wafer surface. Therefore, when the film thickness of the lower cladding layer 522 is 1.5 μm, a gap in height between the core layer 53 and the pedestal block 59 is only 15 nm. Thus, it is possible to perform optical coupling with high accuracy without performing optical axis adjustment, by adjusting a horizontal direction with the alignment marker 60, and mounting the light emitting device 58 on the pedestal block 59. More specifically, an active layer 581 of the light emitting device 58 and the core layer 53 become opposed with high accuracy. Incidentally, in FIG. 4, a heat treatment temperature of each individual operation is indicated.
The film made by the plasma CVD can have a high refractive index, and so it is possible to increase a refractive index difference between a core and a cladding, to significantly improve the flexibility in design. However, a thin film formed by the plasma CVD requires a heat treatment at a high temperature, normally around 1,100° C.
In the optical waveguide device 50, the core layer 53 is the atmospheric CVD film as previously described. This is because, if the core layer 53 is a plasma CVD film, the chromium film 61 is oxidized by the heat treatment at a high temperature, and the pedestal block forming mask 62 no longer functions correctly.